The present invention relates to a joystick controller, in particular to a joystick controller for a portable radio communication device.
A joystick controller may typically be characterised as a hand held device which can control the position and the movement of some object or thing that is remote from the joystick. Joysticks are widely used in electronic/electrical environments, for example, in computer games to control the movement of an on-screen image, in robotics to control the positioning of a robot arm, and recently in laptop computers as selection devices. Common to all joystick applications is that the user relies on his hand-eye co-ordination to effect and control the position and movement of the remote object.
With so many different joystick applications presently in use, there are available a correspondingly great many different designs of joystick controllers. In the main, a conventional joystick controller comprises a joystick lever or handle upstanding from a housing base, the lever being constrained so as to rock from side to side, up and down and in intermediate positions thereof in relation to the housing base. The joystick lever is effectively mounted on a ball joint with respect to the housing base, and can thereby pivot around any rotational axes in the base plane. In analogue joysticks the pivoting movement of the joystick lever is detected by a series of strain gauges provided in the housing base, which output electrical signals correlating to the sensed movement. These output electrical signals are used to control the remote object. Digital joysticks make use of on/off contacts and are therefore generally smaller in size than analogue joysticks. Spring bushings and such like are arranged in the housing and connected to the lever to return the lever back to its balanced upright position when it is released by the user.
In the field of mobile communications, and in particular mobile telephones, it is envisaged that joystick controllers could be used to provide a quick and convenient means for the user to interact with a mobile telephone, for example to navigate through the variety of menu options, or for use in browser applications. However, because of their relatively bulky and intricate design, known analogue joysticks do not readily lend themselves to mobile telephone applications. It is therefore an aim of the present invention to provide an improved joystick controller, particularly one that is apt for use in a radiotelephone.
Accordingly the present invention resides in a joystick controller for a portable radio communication device wherein the controller or the device provides a housing, and wherein the controller comprises a control member adapted for actuation by a user and mounted in relation to the housing for pivotal movement therebetween, electrical contact points provided on a printed circuit board and supported in the housing spaced from the control member and outputting an electrical signal when conductively bridged, and elasto-resistive material which in a relaxed state is an electrical insulator, and in a stressed state is an electrical conductor, disposed between, and in contact with, the control member and the electrical points; the arrangement being such that when there is no force applied by the user on the control member it is in an equilibrium position and accordingly does not apply stress on the elasto-resistive material and accordingly the electrical contact pads are on open circuit, and when a force is applied by the user to the control member it is in a non-equilibrium position and accordingly applies a stress on the elasto-resistive material and accordingly the electrical pads are on closed circuit, wherein in the non-equilibrium position the elasto-resistive material conducts current proportionally in response to the degree of stress applied on the elasto-resistive material by the control member, whereby the amount of current conducted is indicative of the position of the control member in relation to the elasto-resistive material.
A joystick controller of the present invention presents a number of advantages over prior art joysticks, in particular prior art analogue joysticks. It is found that the use of elasto-resistive material as a transducer between movement of the control member and the output of electrical signals affords a more compact and lighter joystick controller design. Such a design obviates the need for strain gauge sensing devices, and thus their associated complexity and expense. Accordingly, there are far fewer constraints on the actual form or shape the joystick controller can take, and as a result increases the freedom for design. Thus, the present invention provides for a simplified solid state, low cost joystick controller which can be used for rapid operation e.g. as a pointing device for an on-screen cursor of a mobile phone, or a scrolling function on a menu based user interface of a mobile phone.
An advantage of using the ER material is that because the electrical current induced across the contact pads is proportional to the mechanical load applied to the lever, an analogue signal is produced, which is suitable for cursor control in browser type applications. This is because the electrical resistance of the ER material is dependent on the degree to which it is subjected to distortion forces.
In a preferred embodiment, the force applied to move the control member is 2 Newtons. As the applied force increases so the resistance of the ER material decreases
Advantageously, the ER material comprises resilient bias means. The resilient bias means is adapted to act on the joystick control lever in such a manner so as to retain the control lever in a first position in which its orientation is substantially orthogonal to the plane of the ER material, and in which the forces exerted by the resilient means are in an equilibrium condition. When the control lever is moved by the user it attains a second position displaced from the first position in which the forces exerted by the resilient bias means are in a non equilibrium condition and act to apply a urging force to return the control lever to its first position. Accordingly, a joystick controller of the: present invention is not encumbered by spring bushings or other such bias arrangements ordinarily necessary to return the control lever to its equilibrium position.
The elasto-resistive material may be a polymer composition comprising electrically conducting particles encapsulated within an electrically insulating elastomer, the ratio of the conducting particles to the non-conducting elastomer being such that the electrical resistivity of the material varies in a linear manner in response to the application of force to the material.
The conductive filler may be a metal powder such as Ni INCO 287. The elastomer may be a silicone elastomer based on polydimethylsiloxane and having a low surface energy, and being high on the triboelectric series. The modifier may be fumed silica.
Conveniently, the ratio of conductive filler to elastomer is in the range 1:1 to 3:1.